Cellulose ester films have excellent transparency and can easily be made into films having small refractive-index anisotropy, and are therefore widely used for optical applications, such as protective films for polarizing plates.
Optical films, however, are generally exposed over a prolonged time to ultraviolet rays contained in sunlight as well as ultraviolet rays contained in light sources of display devices. Accordingly, optical films turn yellowish over time and thus suffer from degradation in display quality.
Further, polarizing plates for LCDs used for gauges and indicators of automobiles, for example, also need to be heat resistant.
For these reasons, conventional optical films contain ultraviolet absorbers and anti-weathering agents. For example, Patent Document 1 proposes a method of adding a benzophenone-based ultraviolet absorber to a cellulose ester film. Patent Documents 2 to 8 propose methods of adding benzotriazole-based ultraviolet absorbers. Patent Document 9 proposes a method of adding benzotriazole-based and triazine-based ultraviolet absorbers and a hindered amine-based light stabilizer to prevent degradation and discolouration of films.
The longer life of LCDs, however, requires further improvement in weather resistance.
Citation List
Patent Document
Patent Document 1: JP-A-6-118233
Patent Document 2: JP-A-6-130226
Patent Document 3: JP-A-2000-193821
Patent Document 4: JP-A-2001-154017
Patent Document 5: JP-A-2002-169020
Patent Document 6: JP-A-2003-176366
Patent Document 7: JP-A-2007-108775
Patent Document 8: JP-A-2007-169590
Patent Document 9: JP-A-2001-072782